1. Field of the Invention
The present invention relates to fiber optic switches and, more particularly, to a switch wherein the optical fibers to be switched are coupled by a butt joint and are rotated relative to each other about an axis offset from an axis through the butt-joined fibers in order to effect switching.
2. Description of the Prior Art
There has been a long-standing need for a relatively inexpensive but precise fiber optic switch. It has been recognized that a key component needed for the practical implementation of optical fiber local area networks is a precision fiber optic switch, particularly a switch that can perform a bypass function.
Historically, fiber optic switches have been difficult to build because of the accurate mechanical alignment which must be maintained between the cores of the optical fibers being switched. Such precise alignment must be maintained in extreme environmental conditions and over many operating cycles.
Numerous schemes have been used to provide a precision fiber optic switch, and while some of these have proven somewhat successful, a low-cost precision switch has not yet been developed. Butt-joined optical fibers are usually switched by linear translation of the fibers relative to each other. In this type of switch considerable difficulty is experienced in attempting to attain the desired precision. Another switching technique makes use of an expanded-beam optical coupling between two fiber cores where switching is effected by manipulation of the optical beam between the fibers using devices such as lenses, prisms, gratings or mirrors. This type of switch becomes complex and expensive.
Mechanical type switches rely on displacing a fiber or a physical body containing the fiber to connect or disrupt the passage of light from one fiber to another. The optical fiber switch depends on the transverse mechanical motion of the fiber within a guide mechanism. Such fiber optic switches have been provided for switching a single optical fiber, or in the form of a multi-fiber switch array; however, the desired precision has not been achieved with consistency, and the switch is very sensitive to environmental conditions, particularly vibration.
Another type of mechanical switch is based on the electro-wetting effect wherein the switch operates by moving a mercury slug into and out of a collimated beam of light leaving a lens to allow the light to enter another similar lens or to reflect the light back through the lens to another optical fiber.
Several types of electro-optic switching mechanisms have been employed using such schemes as a frequency-tunable cleaved coupled cavity laser and a grating de-multiplexer. Pure optical switches have also been suggested for use in conjunction with magnetic fields employing Faraday rotation.
More recent attempts have been made to design optical fiber switches utilizing the switching effect of liquid crystals.
While some of these techniques hold great promise, they are extremely sophisticated and complex, resulting an unacceptably high cost and questionable reliability.